一、epoll服务端实现中需要的3个函数：
- epoll_create：创建保存epoll文件描述符的空间。
- epoll_ctl：向空间注册并注销文件描述符。
- epoll_wait：与select函数类似，等待文件描述符发生变化。
二、示例
回声服务端：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h> #define BUF_SIZE 1024
#define EPOLL_SIZE 50
void error_handling(char * messages); int main(int argc, char *argv[])
{
if(argc != )
{
printf("Usage : %s <port>\n", argv[]);
exit();
}
int serverSock, clientSock;
struct sockaddr_in serverAddr, clientAddr;
socklen_t clientAddrSize; char buf[BUF_SIZE];
int strLen; struct epoll_event *ep_events;
struct epoll_event event;
int epfd, event_cnt; serverSock =socket(PF_INET, SOCK_STREAM, );
if(serverSock == -)
error_handling("socket() error"); memset(&serverAddr, , sizeof(serverAddr));
serverAddr.sin_family = AF_INET;
serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
serverAddr.sin_port = htons(atoi(argv[])); if(bind(serverSock, (struct sockaddr*) &serverAddr, sizeof(serverAddr)) == -)
error_handling("bind() error");
if(listen(serverSock, ) == -)
error_handling("listen() error"); epfd = epoll_create(EPOLL_SIZE);
ep_events = (struct epoll_event*)malloc(sizeof(struct epoll_event) * EPOLL_SIZE); event.events = EPOLLIN;
event.data.fd = serverSock;
epoll_ctl(epfd, EPOLL_CTL_ADD, serverSock, &event); puts("Server start...");
while(){
event_cnt = epoll_wait(epfd, ep_events, EPOLL_SIZE, -);
if(event_cnt == -){
puts("epoll_wait() error");
break;
}
for(int i = ; i < event_cnt; i++){
if(ep_events[i].data.fd == serverSock){
clientAddrSize = sizeof(clientAddr);
clientSock = accept(serverSock, (struct sockaddr*)&clientAddr, &clientAddrSize);
event.events = EPOLLIN;
event.data.fd = clientSock;
epoll_ctl(epfd, EPOLL_CTL_ADD, clientSock, &event);
printf("connected client: %d\n", clientSock);
}
else{
strLen = read(ep_events[i].data.fd, buf, BUF_SIZE);
if(strLen == ){
epoll_ctl(epfd, EPOLL_CTL_DEL, ep_events[i].data.fd, NULL);
close(ep_events[i].data.fd);
printf("closed client: %d\n", ep_events[i].data.fd);
}
else{
write(ep_events[i].data.fd, buf, strLen);
puts("echo");
}
}
}
}
close(serverSock);
puts("Server close...");
return ;
} void error_handling(char * messages)
{
puts(messages);
exit();
}
三、条件触发和边缘触发
条件触发方式中，只要输入缓冲有数据就会一直通知该事件。
边缘触发方式中输入缓冲收到数据时仅注册一次该事件。即使输入缓冲中还留有数据，也不会再进行注册。
select模型是以条件触发的方式工作的。
epoll默认是以条件触发方式工作的。
若将文件（套接字）改为非阻塞模式。调用read&write函数时，无论是否存在数据，都会形成非阻塞文件（套接字）。
边缘触发方式下，以阻塞方式工作的read&write函数又可能引起服务器端的长事件停顿。因此，边缘触发方式中一定要采用非阻塞read&write函数。
边缘触发的回声服务端：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <errno.h> #define BUF_SIZE 4
#define EPOLL_SIZE 50
void setnonblockingmode(int fd);
void error_handling(char * messages); int main(int argc, char *argv[])
{
if(argc != )
{
printf("Usage : %s <port>\n", argv[]);
exit();
}
int serverSock, clientSock;
struct sockaddr_in serverAddr, clientAddr;
socklen_t clientAddrSize; char buf[BUF_SIZE];
int strLen; struct epoll_event *ep_events;
struct epoll_event event;
int epfd, event_cnt; serverSock =socket(PF_INET, SOCK_STREAM, );
if(serverSock == -)
error_handling("socket() error"); memset(&serverAddr, , sizeof(serverAddr));
serverAddr.sin_family = AF_INET;
serverAddr.sin_addr.s_addr = htonl(INADDR_ANY);
serverAddr.sin_port = htons(atoi(argv[])); if(bind(serverSock, (struct sockaddr*) &serverAddr, sizeof(serverAddr)) == -)
error_handling("bind() error");
if(listen(serverSock, ) == -)
error_handling("listen() error"); epfd = epoll_create(EPOLL_SIZE);
ep_events = (struct epoll_event*)malloc(sizeof(struct epoll_event) * EPOLL_SIZE); setnonblockingmode(serverSock);
event.events = EPOLLIN;
event.data.fd = serverSock;
epoll_ctl(epfd, EPOLL_CTL_ADD, serverSock, &event); puts("Server start...");
while(){
event_cnt = epoll_wait(epfd, ep_events, EPOLL_SIZE, -);
if(event_cnt == -){
puts("epoll_wait() error");
break;
}
puts("return epoll_wait");
for(int i = ; i < event_cnt; i++){
if(ep_events[i].data.fd == serverSock){
clientAddrSize = sizeof(clientAddr);
clientSock = accept(serverSock, (struct sockaddr*)&clientAddr, &clientAddrSize);
setnonblockingmode(clientSock);
event.events = EPOLLIN|EPOLLET;
event.data.fd = clientSock;
epoll_ctl(epfd, EPOLL_CTL_ADD, clientSock, &event);
printf("connected client: %d\n", clientSock);
}
else{
while()
{
strLen = read(ep_events[i].data.fd, buf, BUF_SIZE);
if(strLen == ){
epoll_ctl(epfd, EPOLL_CTL_DEL, ep_events[i].data.fd, NULL);
close(ep_events[i].data.fd);
printf("closed client: %d\n", ep_events[i].data.fd);
break;
}
else if(strLen < ){
if(errno == EAGAIN)
break;
else
puts("???????");
}
else{
write(ep_events[i].data.fd, buf, strLen);
}
}
}
}
}
close(serverSock);
puts("Server close...");
return ;
} void setnonblockingmode(int fd) // 套接字改成非阻塞的
{
int flag = fcntl(fd, F_GETFL, );
fcntl(fd, F_SETFL, flag|O_NONBLOCK);
} void error_handling(char * messages)
{
puts(messages);
exit();
}